Flame spraying with powder blend of ferromolybdenum alloy and self-fluxing alloys

ABSTRACT

A flame spray powder comprising a mixture of a self-fluxing alloy powder and about 5-95 percent by weight, based on the total thereof with said self-fluxing alloy powder, of a ferromolybdenum alloy comprising by weight about 50 to 75 percent of molybdenum and about 50 to 25 percent of iron, which powder is characterized by forming in its flame-sprayed condition an adherent porous coating on a substrate.

United States Patent [191 Ingham, Jr. et al.

[ FLAME SPRAYING WITH POWDER BLEND OF F ERROMOLYBDENUM ALLOY AND SELF-FLUXING ALLOYS [75] Inventors: Herbert Smith Ingham, Jr.,

Northport; Edward Robert Novinski, Mineola, both of NY.

[73] Assignee: Metco, lnc., Westbury, NY.

[22] Filed: Jan. 18, 1973 211 App]. No.: 324,724

[52] US. Cl. 106/1, 75/.5 BB, 75/.5 BA, 106/15 FP,117/105.2 [51] Int. Cl C23c 7/00 [58] Field of Search 106/15 FP, l; 175/.5 BB, 175/.5 BA; 117/1052 [56] References Cited UNITED STATES PATENTS 3,313,633 4/1967 Longo 106/1 [11] 3,819,384 1 June 25, 1974 Timmons 75/.5 BB Longo 106/1 Primary Examiner-Harry Wong, Jr. Attorney, Agent, or Firm-Burgess, Dinklage &

Sprung [5 7] ABSTRACT 6 Claims, N0 Drawings FLAME SPRAYING WITH POWDER BLEND OF FERROMOLYBDENUM ALLOY AND SELF-FLUXING ALLOYS This invention relates to a flame spray powder mixture containing a self-fluxing alloy powder and a molybdenum-containing powder, to a process for flame spraying such powder mixtures to produce adherent, porous coatings which show excellent wear and loadresistant characteristics, and to the coatings so produced.

In the flame spray art, there is a well known class of powders which are commonly referred to as sprayweldable, self-fluxing metal powders, or simply as selffluxing alloy powders. Such powders are, for example, described in US. Pat. No. 2,875,043 of Feb. 24, 1959 and U.S. Pat. No. 2,936,229 of May 10, 1960. These powders contain a base metal, such as nickel or cobalt, and a constituent to provide fluxing properties, such as boron or preferably boron and silicon. The powders are most frequently used for applying fused coatings to steel or steel-alloy bases by a process known as spray welding. The spray-welding process involves the steps of first spraying the powder onto the surface to be coated, using the conventional flame-spray process, and thereafter fusing the coating in place. The fusing may be done, for example, in a furnace, by means of induction heating or the like, but is often done by directly heating the coated surface with a heating torch.

The flame spraying in the sprayweld process is simply a mode of positioning the alloy powder on the surface to be coated in order to allow the fused coating to be formed by the subsequent fusing operation. The coating thus sprayed prior to the fusing operation is porous, is not firmly bonded in place, and is not useful in the same manner as subsequent fused coatings, i.e. is not a hard, dense, wear-resistant surface. The particles of a ground-finished, as-sprayed coating, will for example pull out when pressure-sensitive tape, such as Scotch tape, is applied and then stripped off.

U.S. Pat. No. 3,3l3,633 of Apr. ll, 1967 and U.S. Pat. No. 3,378,392 of Apr. 16, 1968 disclose flame spray powder mixtures containing a self-fluxing alloy powder which may be sprayed, under special conditions of temperature, to produce dense, coherent coatings which are similar in certain respects to fused coatings formed by the sprayweld process but which do not require a subsequent fusing operation. In addition to the self-fluxing alloy powder the powder mixture contains about 5 to 95 percent by weight and preferably to 30 percent by weight, or alternately 70 to 90 percent by weight, of a metal powder selected from the group consisting of tungsten, rhenium, tantalum, molybdenum, columbium, and alloys thereof. Utilizing a plasma flame spray process these powder mixtures produce dense coherent coatings which are similar in certain respects to fused coatings formed by the sprayweld process but which do not require a subsequent fusing operation. The coatings show superior properties as bearing and other wearand load-resistant surfaces.

The coatings are entirely satisfactory for most purposes but the cost is relatively high and the required temperatures are quite high, often exceeding 4,000 F and sometimes even 6,000 F. For some purposes, however, even greater wear resistance is desired and a certain level of porosity.

It is accordingly an object of the present invention to provide flame spray powders which produce coatings performing as well as fused coatings without, however, requiring a subsequent fusing operation.

Another object of the invention is to provide hard coatings of substantial density which still are porous enough to retain oil.

It is a further object to provide relatively inexpensive flame spray powders of the class described.

A further object of this invention is a process for producing dense, wearand load-resistant coatings, utilizing a flame spray powder mixture containing a selffluxing alloy powder.

Still another object is to provide flame spray powder mixtures which may be sprayed at lower temperatures than heretofore and yet provide coatings of desired properties.

These and other objects and advantages are realized in accordance with the present invention wherein there is provided an improvement in the spray-welding process of US. Pat. Nos. 3,313,633 and 3,378,392 in which a self-fluxing alloy powder is flame sprayed onto a surface along with a high melting powder comprising about 5 to percent by weight of the self-fluxing alloy and high melting powder. The improvement comprises using as said high melting powder a ferromolybdenum alloy comprising by weight about 50 to 75 percent of molybdenum and about 50 to 25 percent of iron, which powder is characterized by forming in its as flamesprayed condition an adherent porous coating on a substrate. The ferromolybdenum alloy preferably comprises about 58 to 65 percent of molybdenum, up to about 3 percent and preferably less than about 2.5 percent of carbon, less than about 5 percent of foreign materials such as silicon, cooper, sulfur and/or phosphorus, and the balance iron. The cost of such ferromolybdenum alloys is only a fraction of the cost of molybdenum per se, e.g. about 1/3 to H4 the price, and'yet the performance is generally comparable and even superior in certain respects. Depending upon the specific composition the melting point of the ferromolybdenum alloy may exceed 3,500 F, may be slightly below it or even or 200 F lower if the molybdenum content is at the lower end of the range.

The coating is not self-fusing but is quite dense, although not so much so as with unalloyed molybdenum. The porosity of the coating may range up to about 10 percent or even higher but prefereably is about 5 percent, making it oil-retaining and thus especially suited for certain applications, e.g. coated machine elements, piston rings, and the like, described more fully hereinbelow.

As described in US. Pat. Nos. 3,313,633 and 3,378,392, the self-fluxing alloy powder used in accordance with the invention may be any known or conventional self-fluxing alloy powder, as for example, any of the powders described in US. Pat. Nos. 2,875,043 and 2,936,229. These powders are often referred to as selffluxing sprayweld or spray-weldable powders but the term self-fluxing alloy powders will be generically used herein and in the claims to designate these materials. The self-fluxing alloy powders are preferably of the nickel or cobalt type containing boron, and most preferably boron and silicon as the self-fluxing element. The most preferable self-fluxing alloy powders are of the nickel or nickel-chromium alloy type containing boron and silicon. In addition to the base metal, i.e., the

nickel and/or cobalt and the fluxing element or elements, the powder may be formed of additional alloy components, as for example up to 20 percent chromium, to impart corrosion and oxidation resistance, carbon in an amount of not more than a few percent, iron in an amount not exceeding about percent, and preferably not exceeding about 5 percent in weight of the total alloy.

An example of a typical self-fluxing alloy powder of the boron-nickel type consits of 0.7-1 percent carbon, 3.5-4.5 percent silicon, 2.75 to 3.75 percent boron, 3-5 percent iron, up to 18 percent chromium, as for instance 16-18 percent chromium, with nickel making up the balance.

An example of a typical sprayweld alloy of the cobalt base type may, for example, contain 1 /2 to 3 percent boron, 0-4.5 percent silicon, 0-3 percent carbon, 0-20 percent chromium, 0-30 percent nickel, 0-20 percent molybdenum, 0-20 percent tungsten, and the balance cobalt.

The self-fluxing and ferromolybdenum alloy powders should generally have a particle size below 80 mesh US. Standard screen size. When intended for spraying with a plasma flame in accordance with the preferred embodiment of the invention, the particles should be of a size between 80 mesh and +0.5 micron. As is usual for flame spray powders, a narrower size range is preferable, whether in the fine or coarse portion of this wide range. The self-fluxing alloy is preferably between 230 mesh and microns/The ferromolybdenum is preferably between 170 mesh and +15 microns. It is optionally desirable for the size of both powders in a blend to be +5 microns.

The high melting point molybdenum-containing powder must be present in an amount of about 5 to 95 percent by weight and preferably 15 to percent, or alternatively 70 to 90 percent by weight based on the total weight of the mixture thereof with the self-fluxing alloy powder.

The powder mixture in accordance with the invention is preferably sprayed per se but may be sprayed in admixture or in conjunction with other spray materials, as for example other high melting powders such as one or more of tungsten, rhenium, tantalum, columbium and/or their alloys as well as molybdenum alone or alloyed other than with iron as described herein; aluminum; or refractory carbides, such as carbides of tungsten, tantalum, titanium, etc., with or without a cobalt or nickel matrix; refractory oxides, such as aluminum oxide or zirconium oxide, molybdenum disilicide, exothermic composite powders such as described in US. Pat. No. 3,322,515, etc. The powder mixture in accordance with the invention may, for example, be sprayed in amounts of 5-95 percent, or preferably 10-90 percent, by weight of the other spray material, said percentage being based on the total mixture.

The powder mixture is preferably sprayed in a powder type flame spray gun such as a combustion flame spray gun but must be sprayed under conditions of temperatures which will cause melting of the high melting point metal powder component. For this purpose the temperature in the heating Zone should exceed 4,000 F and should preferably exceed 7,000 F.

The spraying in accordance with the invention is preferably effected with a plasma flame spray gun, as for example of the type which produces a plasma flame by constricting an electric arc in a nozzle with a plasma-forming gas, for instance nitrogen or argon alone, or in mixture with hydrogen. Guns which produce a plasma flame in this manner are, for example, described in US. Pat. No. 2,960,594.

lt is also possible to effect the spraying in a wiretype gun, with the powder mixture held in a spray wire or rod shape by a binder, as for example, a synthetic plastic, for example in the manner described in US. Pat. No. 2,570,649 of Oct. 9, 1951. The term powder as used herein is generically intended to designate not only powder in a loose form, but powder in such bonded form. In such case the wire-type gun must utilize a flame of sufficient temperature. to melt the high melting point metal, as for instance a plasma flame.

In addition to simple blends of mixtures of powders, composite particles containing the ferromolybdenum and self-fluxing alloy powders may be used. Thus for example, ferromolybdenum particles of the above mentioned type, but coated with finer particles of the selffluxing alloy may be used. For this purpose, the selffluxing alloy may be in the form of a very fine powder or dust as for example having a particle size between about 25 and 0.5, and preferably between 10 and 1 microns, which is bonded to the surface of ferromolybdenum as for example with a binding agent such as a phenolic resin binding agent or any other organic binding agent or is simply thermally bonded or bonded in any other manner to the ferromolybdenum.

Alternately, the individual particles may be selffluxing alloy particles of size suitable for'flame spraying, but coated with finer particles of the ferromolybdenum. In this case the latter is in the form of a very fine powder of dust such as between about 25 and 0.5 and preferably between 10 and 1 microns. Similar binding means as described above may be used.

The powder may also comprise individual composite grains containing sub-particles of both the self-fluxing alloy and ferromolybdenum. Both the alloy and ferromolybdenum sub-particles may be in the form of a very fine powder or dust as for example having a particle size between 25 and 0.5 and preferably between 10 and 1 microns. The aggregate particles may be formed or briquetted or tableted from the finer particles by conventional powder metallurgy techniques with or without a bonder, or by spray drying, as for example described in US. Pat. No. 3,617,358.

In all other respects the spraying is effected in the well-known and conventional manner for flame spraying, particularly for flame spraying with a plasma flame spray gun.

The coatings may be formed on conventional surfaces, as for example iron and steel alloyed surfaces for any purposes which require a wearand/or loadresistant surface. Coatings of a depth of between .0005 and 0.125 inch and preferably between .002 and 0.030 inch may be formed, and are extremely useful as wear resistant surfaces, as for example on internal combustion engine piston rings. The coatings in accordance with the invention may also be used for crankshafts roll journals bearing sleeves impeller shafts gear journals fuel pump rotors screw conveyors wire or thread capstans -Contmued brake drums shifter forks doctor blades thread guides farming tools motor shafts lathe ways lathe and grinder centers cam followers cylinder liners.

The surface which is sprayed in accordance with the invention should be prepared in the well known and conventional manner for flame spraying, for example with steel grit propelled with air at a pressure of 100 lbs. per square inch, or surface treated in any other conventional manner, as for example rough-threading, coating, or the like. A conventional bond coat material may be used such as flame sprayed molybdenum, molybdenum alloy, or nickel aluminide as described in U.S. Pat. No. 3,322,515. In addition to iron and steel, cooper, brass, aluminum, titanium, molybdenum, or any other material whose surface is suitable for flame spraying by conventional methods, may be coated with the powder and by the process in accordance with the invention.

While the coatings produced in accordance with the invention may be substituted in their as sprayed condition for the fused coatings produced by the sprayweld process, they are not identical to these fused coatings, and in certain respects are superior thereto. The structure is different, in that individual high melting point metal particles can usually be individually identified in metallographically prepared sections and porosity is higher. While the coatings in accordance with the invention do not require a subsequent fusing operation and are generally utilized without fusing, the same may be fused or heat-treated in many cases, forming a desirable, high-melting alloyed coating.

The following examples are given by way of illustration and not of limitation:

EXAMPLE 1 Selffluxing alloy: 230 mesh to microns Weight 7r B 3.5 Si 4 Fe 4 Cr 17 C 1.0 Ni Balance High Melting Powders (a) Low carbon ferromolyhdcnum alloy: l00 to +325 mesh Weight 71 Mo -62.5 C -.075

Si 48 v.

-Continued Fe Balance (b) Ferrochrome alloy: Shieldalloy No. 2916 Weight 72 Cr 66.7 C 6.4 Si 2 Fe Balance (c) Chromium: Metco XP 1101 Cr 99.9 wt.% (d) Molybdenum: l to +325 The powders were blended as indicated and sprayed under the conditions set forth in Table l to produce coatings which were tested for abrasion resistance as follows:

1. Measure the thickness of the test buttons (including coating) in four places, using a Supermicrometer, and record the readings. (Locate the four points for a subsequent measurement by placing marks or numbers on the periphery of the button.)

2. Weigh each button accurately, using an analytical balance, and record the weight.

3. Insert a drive assembly in a drill pass spindle.

4. Place a platform scale on the drill press table. Pull the drill press arm (handle) down to a horizontal position and lock it in place.

5. Raise the drill press table until the drive assembly indicates a 25 lb. load on the scale platform.

6. Unlock the drill press spindle. Hang a weight on the press arm, located so as to indicate a 25 lb. reading on the scale. Mark the point on the arm where this reading is obtained.

7. Remove the scale.

8. Raise the spindle and replace the aligning pin with a 1% in. blank pin.

9. Place two test buttons on a wear track. Lower the spindle until drive pins enter the drive holes in the buttons. Lock in place, with no load on the buttons.

10. Start the drill press. Pour into pan a thoroughly mixed slurry of alumina abrasive powder (Metco 101) 270 mesh 15 microns in a slurry of 25 grams of abrasive in 200 cc of light machine oil. Release the lock on the spindle so that the 25 lb. load is applied to the test buttons. Record the starting time.

1 1. Allow the test to run 20 minutes.

12. Remove the buttons and wash them in solvent. Weigh and measure the thicknesses and record the readings for comparison with the original readings.

Hardness values were obtained by standard Rockwell (Ra scale) or Knoop 50 gram load (KHN Porosity was measured by a standard metallographic technique.

The results of the tests are also set forth in Table 1.

gfpo rosgy and excellent wear resistance.

TABLE 1 BLENDS OF 75% HIGH MELTING POWDERS, 25% SELF-FLUXING ALLOY POWDERS Plasma Spray Parameters High Melting Powders (Metco Type 3MB Gun) Ferro- Chromium Molybdenum Low hrome Ferromolybdenum Carbon Nozzle GE GE GE G Current, amps 4 (l0 400 500 300 BLENDS OF 75% HIGH MELTlNG POWDERS, 25% SELF-FLUXING ALLOY POWDERS Plasma Spray Parameters A High Melting Powders (Metco Type 3MB Gun) Ferro Chromium Molybdenum 7 Low A chrome Ferromolybdenum. Carbon N,/H Pressure 50/50 50/50 50/50 50/50 N /H Flow 100/5 100/5 100/15 100/15 Powder Port No. 2 No. 2 No. 2 No. 2 Car. Flow 37 37 37 37 Spray Rate, lbs/hr. 6-8 6-8 10-20 12-13 Spray dist., in. 2-3 2-3 2-3 4 Meter Wheel S S S S Coating Test Results Macrohardness, Ra 77 70 69 70.5 Microhardness, Major Phase 740 646 963 KHN Minor Phase 858 735 'Powder Micro- Major Phase 1563 l 129 hardness,1(HN,-, Minor Phase 912 l 198 Porosity 6.0 3.0 5.5 1.2 Weight loss, of Standard 94 l 15 67 103 Thickness loss,% of. Standard 1 14 141 73 1 18 EXAMPLE 2 While the invention has been described in detail with In place of the ferromolybdenum alloy of Example 1,

there was used a high carbon ferromolybdenum alloy of approximately the same particle size distribution and cost but having the following analysis:

Weight Mo 62.5 C 2.3 Si 1 .1 Cu .09

.l l P .03 Fe Balance phase contained in a larger particle; it is believed if the carbide phase were in smaller particles this tendency would be eliminated.

in comparison trials without the self-fluxing alloy, high carbon ferromolybdenum alloy coatings had high macro hardnesses (R2 65 to 72) and they were relatively porous. The contained carbide type particles with a micro hardness of 1,740 to 2,503 KHN In water slurry testing they wore twice as fast as the 75/25 molybdenum/self-fluxing alloy coatings. Dry seizure testresults showed deep scratches in the cast iron plate.

Neat low carbon ferromolybdenum spray coatings, i.e., free of self-fluxing alloy, wore much more rapidly in water slurry testing than the blend.

reference to certain specific embodiments, various changes and modifications which fall within the spirit of the invention and scope of the appended claims will become apparent to the skilled artisan. The invention is therefore only intended to be limited by the appended claims or their equivalents wherein I have endeavored to claim all inherent novelty.

What is claimed is:

l. A flame spray powder comprising a mixture of a boron containing nickel or cobalt base self-fluxing alloy powder and about 5-95 percent by weight, based on the total thereof with said self-fluxing alloy powder, of a ferro-molybdenum alloy comprising by weight about 50 to percent of molybdenum and about 50 to 25 percent of iron, which powder is characterized by forming in its flame-sprayed condition an adherent porous coating on a substrate.

2. A flame spray powder according to claim 1 wherein said ferromolybdenum alloy comprises up to about 3 percent by weight of carbon.

3. A flame spray powder according to claim 1 in which said ferromolybdenum alloy is present in amount of about 15-30 percent.

4. A flame spray powder according to claim 2 in which said ferromolybdenum alloy is present in amount of about 70-90 percent.

5. A flame spray powder according to claim 2 having a particle size between mesh and +0.5 micron.

6. A flame spray powder according to claim 2 having a particle size between mesh and +15 microns.

5 0mm!) 51mm iAIElH UH'IQE e CERTIFICATE OF CORRECTION Petent: No. 3,819,384 Dated June 25, 1974 Inventofls) Herbert Smith Ingham, Jr. et al.

It is certified that error appears' in the aboye-identlficd patent and that said Letters Patent are hereby corrected as shown below:

Col. 2,1ine 35, change "tamper" to M topper Col. 6, Table l, cancel the heading and substitute therefor the following:

TABLE 1 HHZNDS OF 75' HIGH MFL'HNH POWDl-LRS. 25'7: SELF FLUXINU ALLOY PUWDERS a a Plasma Spray Purnnwlcrs High Melting Powders L L {ML'lcn Type 3MB Gun) Fcrm- (hmmium Carbon M0 yb chrome Ferrnmnlyhdcnum d enum C01. 7, line 45 change The" to They Signed and sealed this 15th day of October 1974.

(SEAL) Attest: I

-'- A T M COY M. GIBSON JR. C. MARDEALL DAEN Agtesting Officer Commissloner of Patents 

2. A flame spray powder accorDing to claim 1 wherein said ferromolybdenum alloy comprises up to about 3 percent by weight of carbon.
 3. A flame spray powder according to claim 1 in which said ferromolybdenum alloy is present in amount of about 15-30 percent.
 4. A flame spray powder according to claim 2 in which said ferromolybdenum alloy is present in amount of about 70-90 percent.
 5. A flame spray powder according to claim 2 having a particle size between -80 mesh and +0.5 micron.
 6. A flame spray powder according to claim 2 having a particle size between -170 mesh and +15 microns. 